A mask is marginally effective at preventing spread of the virus. Add up a million marginals and you get a substantial effect. One problem all along has been that so many people are only concerned with whether a mask helps ME and can't seem to comprehend that it might help others.
That being said, masks are a pain and I don't wear one any more unless I am told to do so which happens in doctors offices and sometimes at work (when I'm not remote). In those cases, I wear them without complaint.